WO2005024396A1

WO2005024396A1 - An apparatus and method for measuring surface properties

Info

Publication number: WO2005024396A1
Application number: PCT/AU2004/001236
Authority: WO
Inventors: Leslie Charles Zeller
Original assignee: The State Of Queensland Through Its Department Of Primary Industries & Fisheries
Priority date: 2003-09-11
Filing date: 2004-09-10
Publication date: 2005-03-17
Also published as: NZ545705A

Abstract

A method and apparatus (1) for measuring the surface properties of a surface is disclosed. The apparatus comprises a rotatable shaft (14) and a ground engaging foot (15) mounted at a lower end of the rotatable shaft (14) for rotation with the rotatable shaft (14), a drive device (7) to rotate the rotatable shaft (14), a measurement device (34) for measuring the torque experienced by the rotatable shaft (14) whilst the shaft (14) is rotating and the ground engaging foot (15) is in contact with the surface and a control device (11) that is able to receive the torque readings measured by the measurement device (34). The apparatus (1) is able to create a profile of torque with respect to angular displacement of said rotatable shaft (14) in order to accurately define the characteristics of the surface under test.

Description

AN APPARATUS AND METHOD FOR MEASURING SURFACE PROPERTIES FIELD OF THE INVENTION The invention relates to the measurement of surface properties. In particular, although not exclusively, the invention relates to an apparatus and method for determining the torsional strength of grass surfaces. BACKGROUND TO THE INVENTION Sports players are highly sensitive to the physical properties of a playing surface, most notably in terms of traction and friction. Friction and traction are the properties that enable the player to make the movements necessary in sports without excessive slipping or falling. Friction applies to smooth-soled footwear and traction applies to footwear having studs, cleats, or spikes to provide extra grip.

Friction of a surface is normally expressed in terms of its coefficient (μ),

which is the ratio of the frictional force to the vertical force applied. In the case of traction, there is no such well established law but similar principles apply and a coefficient of traction can also be calculated using the equation used to calculate the coefficient of friction. Frictional and tractional coefficients can be considered in terms of either the force required to initiate motion, referred to as the static coefficient, or the force required to maintain motion once started, referred to as the dynamic coefficient. These properties are especially important for turf surfaces as friction and traction vary between turf types and indeed between different fields of the. same turf type. By being able to accurately and repeatedly measure the friction and traction of turf surfaces, values can be identified for these properties that maximise the player's performance and minimize the risk of injury. A device that is commonly used to test the properties of grass has a vertical bar that has a ground engaging member attached at its lower end and a torque wrench attached at it's upper end. A weight is located on an upper side of the ground engaging member. In use, the ground-engaging member abuts the ground with the weight applying a normal force with respect to the ground. The torque wrench is then turned, and thus the ground-engaging member is operatively turned. The maximum torque required to initiate the turning of the ground engaging member is measured. The static and dynamic coefficient of friction can thus be calculated from this reading. The torque wrench uses the bending characteristics of a cantilever to produce a value of maximum torque per test and is susceptible to errors due to variations of loading points and operational techniques. The accuracy of the data may also be questionable as each operator may use different rotational speeds and may apply different vertical forces when conducting tests.

Additionally, the torque wrench is limited by the resolution of the scale displayed. WO 02/063279 describes a device for measuring the static and/or dynamic friction coefficient of an artificial grass for sports fields. The device has an anchoring body and a vertical bar. The vertical bar has a ground engagement device, such as a football boot, attached at a lower end. The bar is connected to the anchor by means of two horizontal bars. The upper horizontal bar is connected at one end to the upper end of the vertical bar and at the other end to an electrical motor. The lower horizontal bar is attached at one end to the anchoring body and at the other end to the vertical bar approximately halfway between the ground engagement device and the upper horizontal bar. In use the ground engagement device abuts the ground and the electrical motor exerts a horizontal force on the vertical bar via the upper horizontal bar. This creates a bending moment in the vertical bar which is measured by strain gauges present on the lower horizontal bar. In this way, the static and dynamic coefficient of friction for the artificial turf may be tested. WO 2004/051239 discloses a device for measuring the static and/or dynamic friction coefficient of a surface. This device comprises a housing that has a rotatable shaft vertically disposed in the housing. A body is disposed at a lower end of the housing and the body has a surface which is able to be brought into contact with the surface being measured. The device further comprises a measuring means for measuring the torque caused by the friction between the contact surface of the body and the surface to be examined. However the device disclosed in WO 2004/051239 is deficient in that the information that this device displays is limited to the coefficient of friction only.

Hence, only limited analysis of the results may be undertaken and hence the applicability of the device disclosed in WO 2004/051239 to real life surface testing scenarios is limited. For these reasons, it is desirable to provide for a new surface measurement device. OBJECT OF THE INVENTION An object of the invention is to overcome or at least alleviate one or more of the above problems and/or provide the consumer with a useful or commercial choice. SUMMARY OF THE INVENTION In one form, although it need not be the only or indeed the broadest form, the invention resides in an apparatus for measuring the properties of a surface comprising: a rotatable shaft; a ground engaging foot mounted at an end of said rotatable shaft for rotation with said rotatable shaft; a drive device that rotates said rotatable shaft relative to said surface; a measurement device to continuously measure a torque force experienced by said rotatable shaft; and a control device in communication with said measurement device to receive said measurements of torque from said measurement device; wherein, said control device creates a profile of torque with respect to angular displacement of said rotatable shaft. In another form, the invention resides in a method of measuring the properties of a surface including the steps of: (i) exerting a normal force on said surface via a rotatable shaft, said rotatable shaft having a ground engaging foot mounted at an end of said rotatable shaft for rotation with said rotatable shaft; (ii) rotating said rotatable shaft relative to said surface; (iii) continuously measuring a value of torque experienced by said rotatable shaft; and (iv) developing a profile of torque with respect to angular displacement of said rotatable shaft based on said measurements made in (iii). Further features of the present invention will become apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS To assist in understanding the invention and to enable a person skilled in the art to put the invention into practical effect preferred embodiments of the invention will be described by way of example only with reference to the accompanying drawings, wherein: FIG 1 shows a side view of a surface testing apparatus according to one embodiment of the present invention; FIG 2 shows a sectional top view of a drive device comprising part of the surface testing apparatus of FIG 1 ; FIG 3 shows a partial perspective view of the surface testing apparatus of FIG 1 when a shaft of the testing apparatus is in a travel position; FIG 4A shows a sectional top view of a shaft and pipe section of the drive device shown in FIG 2 in a first position; FIG 4B shows a section side view of a shaft and pipe section of the drive device shown in FIG 2 in a first position; FIG 5A shows a sectional top view of the shaft and pipe section of FIG 4A in a second position; FIG 5B shows a sectional side view of the shaft and pipe section of FIG 4B in a second position; FIG 6A shows a sectional top view of the shaft and pipe section of FIG 4A in a third position; FIG 6B shows a sectional side view of the shaft and pipe section of FIG 4B in a third position; FIG 7A shows a sectional top view of the shaft and pipe section of FIG 4A in a fourth position; FIG 7B shows a sectional side view of the shaft and pipe section of FIG 4B in a fourth position; FIG 8A shows a sectional top view of the shaft and pipe section of FIG 4A in a fifth position; FIG 8B shows a sectional side view of the shaft and pipe section of FIG 4B in a fifth position; FIG 9A shows a sectional top view of the shaft and pipe section of FIG 4A returned to the first position; FIG 9B shows a sectional side view of the shaft and pipe section of FIG 4B returned to the first position position; and FIG 10 shows a torque profile generated by the surface testing apparatus of FIG 1. DETAILED DESCRIPTION OF THE INVENTION The method and apparatus of the present invention attempts to overcome at least some of the deficiencies of the prior art by providing a surface testing apparatus that delivers an in depth information profile in order that the surface under test may be characterized more accurately. FIG 1 shows a side view of a surface testing apparatus 1 according to an embodiment of the present invention. Surface testing apparatus 1 comprises a frame 2 having a plurality of lower support members 3, a plurality of upper support members 4 and a plurality of upright support members 5. A plurality of wheels 6 support frame 2. Support plate 20 is mounted on frame 2 and pipe section 35 is operatively mounted on frame 2 as shown. A sensor 44 is operatively mounted on frame 2 adjacent to pipe section 35 as shown in FIG 1.

Preferably, sensor 44 is a limit switch. Optionally, sensor 44 may be a digital encoder having a photo transistor and a light source or similar such sensing device. Surface testing apparatus 1 further comprises drive device 7, testing device 8, lifting arm 9, battery 10, control device 11 , laptop 12 and indicator 13.

Preferably, indicator 13 is a limit switch although it will be appreciated that indicator 13 may be a digital encoder, an infrared sensing device or the like.

Drive device 7 is operatively mounted on frame 2. In FIG 1 , drive device 7 is shown in phantom and its features will be discussed in more detail below. Testing device 8 has a rotatable shaft 14, ground engaging foot 15, fingers 16, weights 17, lifting plate 18 and pins 19. The ground engaging foot 15 is located at a lower end of rotatable shaft 14 and rotates with the shaft 14.

Preferably, zero or more fingers 16 protrude outwardly from ground engaging foot 15. Fingers 16 are releasably attached to ground engaging foot 15 by screwing the fingers into threaded recesses (not shown) located on an underside of ground engaging foot 15. Optionally, fingers 16 are releasably attached to ground engaging foot 15 by means of other attachment means known in the art. Weights 17 are mounted on rotatable shaft 14 above ground engaging foot 15. Preferably, weights 17 have a total mass of 40 kg although it will be appreciated that other masses may be used. Shaft 14 has two wings 37 (not shown in FIG 1 ) extending outwardly from a central portion. Preferably, wings 37 extend outwardly from diametrically opposite sides of the shaft 14. Lifting plate 18 is attached to shaft 14 and extends circumferentially around shaft 14. Lifting plate 18 has a diameter greater than that of shaft 14 as shown. Two pins 19 protrude outwardly from diametrically opposite sides of an upper end of shaft 14 as shown. It should be noted that only one pin 19 is visible in the plan view of FIG 1. Optionally, one pin may extend through shaft 14 with each of its ends protruding from opposite sides of shaft 14. Rotatable shaft 14 is moveable between a testing position and travel position. In the testing position ground engaging foot 15 abuts the ground (not shown) 8. In the travel position, as seen in FIG 1 , the ground-engaging foot 15 is suspended above the ground (not shown) and is supported by the contact of pins 19 on an upper surface of support plate 20. This arrangement will be discussed in more detail below. Lifting arm 9 has forks 21 , L-member 22 and handle member 23. L- member 22 is pivotally mounted on frame 2 via bolt 24 extending between upper members 4 (of which only one is shown in FIG 1 ) of frame 2. Forks 21 are mounted at a lower end of L-member 22 and partially encompass shaft 14 as shown. Handle member 23 is pivotally attached to L-member 22 via bolt 25 extending through both L-member 22 and handle member 23. Battery 10 is electrically attached to control device 11 and control device 11 is electrically attached to drive device 7. Additionally, drive device 7 is in electrical communication with control device 11 and control device 11 is in electrical communication with laptop 12. Furthermore, indicator 13 and sensor 44 are in communication with control device 11. Two guides 50 are located on diagonally opposite sides of frame 2. A spike 51 extends through an aperture of each guide. Preferably, an internal surface of each guide 50 is threaded and each spike 51 has a corresponding thread. As such, each spike 51 is moveable within their respective guides 50 between an upper position and a lower position. In the lower position a lower end of each spike 51 is embedded within the ground (not shown) to anchor surface testing apparatus 1. Optionally, each spike 51 is slideably moveable within each guide are fixed in the upper position by means of a pin or the like. FIG 2 shows a sectional top view of the drive device 7 which is shown in phantom in FIG 1. Drive device 7 has motor 26, sprockets 27, 28 and 29, a test sprocket 30, a drive sprocket 31 , a first chain 32, a second chain 33, pipe section 35 and a measurement device 34. Preferably, measurement device 34 is in the form of a load cell. Optionally, measurement device 34 is any type of measurement device able to measure a force and communicate the force measured. Motor 26 is operatively mounted on frame 2 (not shown in FIG 2) and is operated by control device 11 via cable 36. Preferably, motor 26 is a 24 volt DC motor but it will be appreciated that other forms of motors may be used such as pneumatic, fuel and the like. Sprocket 27 is attached to and rotatable by motor 26. Sprocket 28 is mounted on a lower end of shaft 36. Shaft 36 is operatively mounted on frame 2 (not shown in FIG 2) and is rotatable. The contact between shaft 36 and its mounting is facilitated by means of bearings as is known in the art. Sprocket 28 is in mechanical communication with sprocket 27 via the first chain 32. Hence, as sprocket 27 is rotated by motor 26, sprocket 28 is operatively rotated by motor 26. Sprocket 29 is mounted on an upper end of shaft 29. Hence, when sprocket 28 is operatively rotated by motor 26, sprocket 29 is rotated due to its mounting on shaft 36. Test sprocket 30 is in mechanical communication with sprocket 29 via the second chain 33 and is fixed circumferentially around shaft 40. Thus, test sprocket 30 is operatively rotated by motor 26. Preferably, test sprocket 30 is an idler sprocket and exerts no force on drive device 7. Shaft 40 is operatively mounted on frame 2 (not shown in FIG 2) and is rotatable. The contact between shaft 40 and its mounting is facilitated by means of bearings as is known in the art. Load cell 34 is operatively mounted to frame 2 (not shown) and is mechanical communication with test sprocket 30. Load cell 34 is able to measure the tension in the second chain 33 as will be discussed in detail below. Drive sprocket 31 is fixed circumferentially around an outer edge of pipe section 35 and is in mechanical communication with sprocket 29 via a second chain 33. Thus, when drive sprocket 31 is operatively rotated by motor 26, pipe section 35 is similarly rotated. As previously mentioned, pipe section 35 is operatively mounted on frame 2 (not shown). As pipe section 35 is rotatable, the contact between pipe section 35 and it's mounting is facilitated by means of bearings as is known in the art. Aperture 39 extends through pipe section 35. Pipe section 35 has a pair of upper members 38 (not shown in FIG 2) extending inwardly within aperture 39. Upper members 38 extend inwardly from diametrically opposite sides of aperture 39 at an upper end of pipe section 35. A pair of lower members 43 (not shown in FIG 2) extend inwardly within aperture 39 of pipe section 35. Lower members 43 extend from diametrically opposite sides of aperture 39 and are offset approximately 90 degrees from upper members 38. Pipe section 35 is adapted to encompass rotatable shaft 14. Shaft 14 extends through aperture 39 in pipe section 35 as seen in FIG 2. Shaft 14 is rotated by pipe section 35, which is operatively rotated by motor 26, by means of contact between the wings 37 mounted on shaft 14 and either upper members 38 or lower members 43 of pipe section 35. Hence, drive device 7 is in mechanical communication with rotatable shaft 14 via the contact between wings 37 and either upper members 38 or lower members 43 of pipe section 35. This will be discussed in more detail below. FIG 3 shows a perspective view of an upper end of shaft 14 when rotatable shaft 14 is in the travel position. Support plate 20 is mounted on upper support members 4 of frame 2. Support plate 20 has an aperture 42 and slots 41 extending outwardly from aperture 42. When rotatable shaft 14 is in the travel position, shaft 14 extends through aperture 42 of support plate 20. Shaft 14 is supported by the contact of pins 19 on an upper surface of support plate 20. When rotatable shaft 14 is moved to the testing position, shaft 14 is rotated such that pins 19 align with slots 41. The pins 19 pass through slots 41 and the shaft 14 moves downwardly under the force of gravity until the ground engaging foot 15 contacts the ground. In the testing position, fingers 16 penetrate the surface of the ground. Hence, the movement of the ground engaging foot 15 from the travel position to the testing position simulates the placement of a persons foot when that person is wearing studded footwear. In use, surface testing apparatus 1 is used to provide detailed information regarding surface properties and in particular the torsional strength of the root systems of turf grasses. Using the torsional strength measurements, the static and dynamic coefficient of friction and traction are measured for a particular surface. Ground engaging foot 15 is rotated about shaft 14 under a normal force provided by weights 17. This movement mimics the movement of a persons foot, for example when playing a sport. The shear strength of the grass is then measured at varying degrees of rotation and a profile is developed that measures the torque vs angular displacement of the ground engaging foot and hence a load profile of the grass is developed. The operation of the surface testing apparatus is controlled from control device 11. An operator moves surface testing apparatus to an area of interest and begins the testing process. Initially, shaft 14 is in the travel position as shown in FIG 3. Hence, pins 19 are in contact with plate 20 and this contact supports shaft 14. FIG 4A shows a sectional top view of pipe section 35 and shaft 14 when shaft 14 is in the travel position. FIG 4B shows a sectional side view of FIG 4A. When shaft 14 is in the travel position wings 37 abut upper members 38 of pipe section 35. The testing process is started by a person pressing a start button (not shown) on control device 11. This causes the control device 11 to start motor 26 and operatively turn pipe section 35. The contact between the upper members 38 of pipe section 35 with wings 37 on shaft 14 causes the shaft to turn. Once the shaft 14 has turned 90 degrees (as shown in FIG 5A and FIG 5B), pins 19 pass through slots 41 on support plate 20. The shaft 14 moves downwardly under the force of gravity until ground engaging foot 15 contacts the ground and fingers 16 embed within the ground. Preferably, the shaft drops 60 millimeters before the ground engaging foot 15 contacts the ground. Optionally, other heights may be used as is appropriate. The force with which ground engaging foot 15 contacts the ground is related to the drop height and the gravitational force of weights 17. As previously mentioned, by varying the drop height and the weights 17, the normal force which ground engaging foot 15 exerts on the ground can be varied. FIG 5B shows the shaft 14 as it is falling. While shaft 14 is falling pipe section 35 is still being operatively rotated by motor 26. During this period the torque experienced by the shaft 14 is calculated. This is accomplished in the preferred embodiment by load cell 34 measuring the tension in the second chain 33 as is known in the art. A person skilled in the art will appreciate that other forms of measurement devices may be used to measure the toque applied to shaft 14 such as digital strain gauges, optical displacement gauges applied directly to the shaft, mechanical displacement gauges applied directly to shaft 14 or the like. There is a direct relationship between the tension in chain 33 and the torque experienced by shaft 14. The torque experienced in shaft 14 has a direct one to one relationship with the resistance that the grass currently being tested is providing to the movement of ground engaging foot 15. Torque is calculated from this force using the equation:

Torque = Force (tension in chain 33) x Radius of drive sprocket 31

Hence, load cell 34 continuously samples (between 10 and 25 samples per second in the preferred embodiment) the tension in the second chain 33 and sends this measurement to control device 11 via data cable 45. Control device 11 calculates the torque measurement and communicates this information to laptop 12 via an RS232 serial communication channel (not shown) for formatting and display. Preferably, control device 11 displays the torque values continuously based on the readings taken from load cell 34. Optionally, control device 11 may display the maximum value of torque only. Preferably, laptop 12 displays the torque values received from control device 11 in a spread sheet application program. As the sleeve rotates from the position shown in FIG 5A and FIG 5B to that shown in FIG 6A and 6B, load cell 34 begins it's measurement of the tension in chain 33. During this period there is no external load being measured as pipe section 35 is not rotating shaft 14. Hence, this allows a calculation of the inherent torque of drive device 7 to be calculated under "no-load" conditions. FIG 6A and FIG 6B show shaft 14 in the testing position. Pipe section 35 rotates the shaft 14 through 180 degrees by lower members 43 contacting wings 37. Hence, shaft 14 is rotated from the position shown in FIG 6A and FIG 6B to that shown in FIG 7A and FIG 7B. During this rotation load cell 34 continues to measure the tension in chain 33 and communicates these value on to control device 11. At this point sensor 44 detects that the shaft has been rotated through

180 degrees and sends a signal to control device 11 alerting the control device 11 that this rotation has occurred. Control device 11 then communicates a stop signal to motor 26. The action of the motor stopping is an indication to the person operating the surface testing apparatus 1 that the test has been completed. At this point, load cell 34 ceases measuring the tension in chain 33. The operator then uses lifting arm 9 to move shaft 14 from the testing position to the travel position. The person pivots handle member 23 until it is substantially parallel with an upper section of L-member 22. At this point handle member 23 locks in place and forks 21 contact a lower side of lifting plate 18. The shaft 14 moves upwardly as lifting arm 9 pivots about bolt 24 and pins 19 pass through slots 41 on support plate 20. As lifting arm 9 is pivoted about bolt 24 during the lifting process a portion of L-member 22 contacts indicator 13. Indicator 13 is in data communication with control device 11 and when control device 11 detects that indicator 13 has been activated control device 11 restarts motor 26. Pipe section 35 then rotates until upper members 35 contact wings 37, as shown in FIG 8A and 8B. In FIG 8A and 8B, lifting arm 9 is still supporting shaft 14. The shaft is then further rotated through to the position shown in FIG 9A and 9B by motor 26. At this point, pins 19 no longer align with slots 41 and hence the weight of shaft 14, ground engaging foot 15 and weights 17 are again supported by the contact of pins 19 with support plate 20 and the shaft 14 is again in the travel position, as shown in FIG 3. In the above testing process, spikes 51 are moved to the lower position and a lower end of each spike embeds within the ground. This anchors the surface testing apparatus 1 in position and prevents the frame 2 rotating about shaft 14. In the preferred embodiment the amount of rotation that the sleeve is undergoing is measured indirectly by time. For example, based on the speed of rotation it takes approximately 10 seconds for one complete rotation of pipe section 35. Hence, in order to move the pipe section 90 degrees from FIG 8A to FIG 9A to enable pins 19 to be offset 90 degrees from slots 41 on support plate 20, the motor is operated for approximately 2.5 seconds by control device 11. Optionally, a digital shaft encoder, in communication with control device 11 , may be fixed on pipe section 35 to directly measure the amount of rotation that pipe section 35 is undergoing. As mentioned, in the preferred embodiment, torque calculations made by control device 11 are sent to laptop 12 for collation. FIG 10 shows a graph of torque vs. samples of three different torque types. Preferably, the x-axis displays the sample number and the y-axis shows the torque measured at that sample number. Hence, by knowing the number of samples made per second and the rotational speed of the shaft, the torque measured at various angles may be calculated. Optionally, the rotation undergone by the shaft may be displayed rather than the sample number. Preferably, fingers 16 are fitted to ground engaging foot 15 to simulate the effect of the movement of a studded boot on the surface. Optionally, fingers 16 may be removed to simulate the effects of the movement of a shoe that does not have studs. It will be understood that the number of fingers 16 and their position upon the underside of the ground engaging foot 15 may be varied to suitably represent different stud configurations of boots. As can be seen in FIG 10, the measurements made by surface testing apparatus 1 can be used to develop torque profiles of grass types and hence a relationship between the maximum torque and the angle of rotation can be created. Additionally, the way in which the grass fails can be analyzed e.g. does the grass fail catastrophically, creating a steep decline in the graph, or does the grass fail gradually, producing a more gradual decline in the graph. In these terms fail means the torque at which the grass stems shear from the topsoil. This level of information is valuable when analyzing grass types and offers a clear advantage over the devices described in the prior art as this information can be used to more accurately characterize the grass that is being tested. Optionally, control device 11 displays the angle that the grass has failed and also the torque at his failure angle. Additionally, the control device 11 stores these details in association with the profile developed. As previously mentioned, the static coefficient of traction can be calculated from these results using known calculation methods. Furthermore, the dynamic coefficient of traction can also be calculated. Similarly, by removing fingers 16, the static and dynamic coefficient of friction can also be calculated.

These details are displayable by control device 11 and are also storeable in association with the profile developed. As the testing process is operated by control device 11 the results are not subject to variation in operational techniques. This ensures that the tests undertaken by surface testing apparatus 1 are repeatable and allow accurate comparison of different grass types and different areas of the same field having the same grass type. In FIG 10 three different grass types are being compared and all grass types have different maximum torques at slightly different angles of rotation. This information allows for accurate comparison of different types of grasses at different locations. Surface testing apparatus 1 provides torque profiles of different grass types. By developing torque profiles and displaying the angle of rotation at which the maximum torque of the grass was measured a more in depth analysis may be undertaken regarding the suitability of grass types for various sporting events. Furthermore, it is widely acknowledged that the surface of a particular field may vary within the field. By testing parts of the field that players feel have different characteristics, a more in depth analysis of the surface of the playing field may be carried out by surface testing apparatus 1 with an aim to identifying preferable surface characteristics. Throughout the specification the aim has been to describe the invention without limiting the invention to any one embodiment or specific collection of features. Persons skilled in the relevant art may realize variations from the specific embodiments that will nonetheless fall within the scope of the invention. For example, weights 17 may be positioned at an upper end of shaft 14. Optionally, weights 17 may be replaced with a hydraulic or pneumatic ram that provides a normal force on the ground via shaft 14. Furthermore, the measurement device, which in the preferred embodiment is load cell 34, may be in the form of a digital strain gauge mounted directly on shaft 14 which measure the torque on shaft 14 directly and are able to communicate torque measurements directly to control device 11. Another variation from the preferred embodiment described above is that laptop 12 may be removed from apparatus 1 and all processing may be carried out at control device 11. Hence, in this embodiment, control device 11 would have persistent storage capabilities and be able to display the torque profiles measured directly. In this embodiment, the results are saved within control device 11 and are communicable to other processing apparatus'. A further variation may be that a mechanical lifting means may replace lifting arm 9 and be directly controlled by control device 11 so that it is not necessary for a person to have to manually lift shaft 14 from the test position to the travel position. This may be facilitated by the use of hydraulic or pneumatic lifting devices. In a further embodiment, surface testing apparatus may be fitted with a GPS receiver in communication with either of control device 11 or laptop 12. Hence, surface testing apparatus 1 may perform multiple tests in a single field and each test may be stored in association with the GPS coordinates of that test. In this way, the variations in surface properties of a field may be analyzed precisely. Additionally, it will be appreciated that the properties of surfaces other than grass may be measured using surface testing apparatus 1. For example, if fingers 16 are removed from ground engaging foot 15, the surface properties of polish wooden floors, tiled floors, bitumen and the like may be measured.

In these instances the coefficient of friction (μ) may be calculated using the equation:

Force = μ x Normal Force.

The value of force is known as it is merely the value of torque multiplied by the mean distance from the shaft to the circumference of the ground engaging foot. Additionally, the Normal Force is known as it is merely the weight of the shaft 14, the ground engaging foot 15 and the weights 17. Hence, the coefficient of friction may be calculated. Similarly, a coefficient for traction may be calculated when surface testing apparatus 1 is carrying out tests on grass with fingers 16 attached. Additionally, the static and dynamic coefficient's of friction and traction may be calculated. These values may be used when undertaking comparisons of different turf types and different areas of a playing field. It will be appreciated that various other changes and modifications may be made to the embodiment described without departing from the spirit and scope of the invention.

Claims

1. An apparatus for measuring the properties of a surface comprising: a rotatable shaft; a ground engaging foot mounted at an end of said rotatable shaft for rotation with said rotatable shaft; a drive device that rotates said rotatable shaft relative to said surface; a measurement device to continuously measure a torque force experienced by said rotatable shaft; and a control device in communication with said measurement device to receive said measurements of torque from said measurement device; wherein, said control device creates a profile of torque with respect to angular displacement of said rotatable shaft.

2. The apparatus for measuring the properties of a surface of claim 1 , wherein said rotatable shaft is moveable between a travel position wherein said ground engaging foot is suspended above said surface, and a testing position wherein said ground engaging foot contacts said surface.

3. The apparatus for measuring the properties of a surface of claim 1 , further comprising a set of weights mounted on said rotatable shaft.

4. The apparatus for measuring the properties of a surface of claim 1 , further comprising a set of weights mounted on said rotatable shaft, said weights exerting a normal force on said surface when said rotatable shaft is in a testing position.

5. The apparatus for measuring the properties of a surface of claim 1 , wherein said control device stores said profile of torque with respect to angular displacement.

6. The apparatus for measuring the properties of a surface of claim 1 , wherein said control device displays said profile of torque with respect to angular displacement.

7. The apparatus for measuring the properties of a surface of claim 1 , wherein said control device calculates a coefficient of friction of said surface.

8. The apparatus for measuring the properties of a surface of claim 7, wherein said control device displays said coefficient of friction.

9. The apparatus for measuring the properties of a surface of claim 7, wherein said control device stores said coefficient of friction in association with said profile of torque with respect to angular displacement.

10. The apparatus for measuring the properties of a surface of claim 7, wherein said coefficient of friction is a static coefficient of friction.

11. The apparatus for measuring the properties of a surface of claim 7, wherein said coefficient of friction is a dynamic coefficient of friction.

12. The apparatus for measuring the properties of a surface of claim 1 , wherein said ground engaging foot further comprises a plurality of fingers.

13. The apparatus for measuring the properties of a surface of claim 12, wherein said fingers are releaseably attachable to said ground engaging foot.

14. The apparatus for measuring the properties of a surface of claim 12, wherein said control device calculates a coefficient of traction of said surface.

15. The apparatus for measuring the properties of a surface of claim 1 , wherein said measurement device is a load cell.

16. The apparatus for measuring the properties of a surface of claim 1 , wherein said measurement device is a load cell and said load cell measures a tension in a drive chain of said drive device.

17. The apparatus for measuring the properties of a surface of claim 16, wherein said torque force experienced by said rotatable shaft is calculated by measuring said tension in said drive chain.

18. The apparatus for measuring the properties of a surface of claim 1 , wherein said measurement device is a digital strain gauge.

19. The apparatus for measuring the properties of a surface of claim 18, wherein said digital strain gauge is mounted on said rotatable shaft.

20. The apparatus for measuring the properties of a surface of claim 1 , wherein said drive device has a motor, a plurality of sprockets and a drive chain in mechanical communication.

21. The apparatus for measuring the properties of a surface of claim 20, wherein operation of said motor is controlled by said control device.

22. The apparatus for measuring the properties of a surface of claim 20, wherein said drive device further comprises a pipe section adapted to encompass said rotatable shaft.

23. The apparatus for measuring the properties of a surface of claim 20, wherein said drive device further comprises a pipe section adapted to encompass said rotatable shaft, said pipe section being rotated by said motor.

24. The apparatus for measuring the properties of a surface of claim 23, wherein said pipe section operatively rotates said rotatable shaft.

25. The apparatus for measuring the properties of a surface of claim 1 , wherein said apparatus further comprises a laptop in communication with said control device.

26. The apparatus for measuring the properties of a surface of claim 1 , wherein said apparatus further comprises a GPS receiver.

27. The apparatus for measuring the properties of a surface of claim 26, wherein said GPS receiver is in communication with said control device, said control device associating said profile of torque with respect to angular displacement of said rotatable shaft with a GPS measurement made by said GPS receiver.

28. A method of measuring the properties of a surface, said method including the steps of: (i) exerting a normal force on said surface via a rotatable shaft, said rotatable shaft having a ground engaging foot mounted at an end of said rotatable shaft for rotation with said rotatable shaft; (ii) rotating said rotatable shaft relative to said surface; (iii) continuously measuring a value of torque experienced by said rotatable shaft; and (iv) developing a profile of torque with respect to angular displacement of said rotatable shaft based on said measurements made in (iii).

29. The method of measuring the properties of a surface of claim 28, wherein said method further includes the step of displaying said profile of torque with respect to angular displacement developed in step (iv).

30. The method of measuring the properties of a surface of claim 28, wherein said method further includes the step of storing said profile of torque with respect to angular displacement developed in step (iv).

31. The method of measuring the properties of a surface of claim 28, wherein said method further includes the step of calculating a coefficient of friction of said surface.

32. The method of measuring the properties of a surface of claim 31 , wherein said method further includes the step of displaying said coefficient of friction of said surface.

33. The method of measuring the properties of a surface of claim 31 , wherein said method further includes the step of storing said coefficient of friction of said surface.

34. The method of measuring the properties of a surface of claim 28, wherein said method further includes the step of calculating a coefficient of traction of said surface.

35. The method of measuring the properties of a surface of claim 34, wherein said method further includes the step of displaying said coefficient of traction of said surface.

36. The method of measuring the properties of a surface of claim 31 , wherein said method further includes the step of storing said coefficient of traction of said surface.

37. An apparatus for measuring the properties of a surface as substantially hereinbefore described with reference to the accompanying figures.